Solar cells generate electricity but at a cost which is too high to compete with electricity from the electric power company. It is generally acknowledged that the solar panel cost will have to drop to approximately $1 to $2 per installed Watt before solar cells can compete in this large potential market. Today's cost for solar panels is in the $6 to $7 per Watt range. Three different approaches have been pursued in attempts to resolve this cost problem.
The conventional approach is to use large silicon solar cells tiled in planar modules where the cell area represents over 80% of the total panel area. The cells in this approach can be single crystal or large grain polycrystalline cells. This approach represents over 90% of the market but the cost of this approach has bottomed out and no further cost reductions are expected.
The second approach is based on the assumption that the cost of silicon wafers is too high and one needs to make low cost thin film cells. The argument is that paint is cheap and that maybe a way can be found to make paints generate electricity. This thin film approach includes amorphous silicon and small grain-size polycrystalline materials like CuInSe2 and CdTe. The problem with this approach has been that destroying the crystal material degrades solar cell performance. To date, this approach has not yielded modules costing less than $8 per Watt.
The third approach is based on concentrating the sunlight onto small single crystal cells using larger inexpensive plastic lenses or metal mirrors. This approach allows more efficient cells to be used and makes good technical sense. However, the problems with this approach are not technical but instead relate to business and politics. Solving the business problems inherent in this approach is the focus of this invention.
Serious attempts to develop solar concentrator photovoltaic systems can again be divided into three parts. First, attempts have been made to use point focus lenses and 30% efficient cells where the systems operate at high concentration ratios, e.g. approximately 500 suns. The problem here is not with the technology. The various components work, and systems have been demonstrated. The problem here is that the investment required to create positive cash flow is too large. Large companies will not take the risk and small companies do not have the resources and the government is not helping. The 30% cells are not being manufactured and investment is required here. Furthermore, trackers with the required accuracy are not being manufactured. Again investment is required. Investment is also required for the thermal management and lens elements. Finally, these systems are not cost effective unless made in large sizes and in large volumes and there are no intermediate markets other than the utility scale market.
The second approach to solar concentrators involves the use of arched linear Fresnel lenses and linear silicon solar cell circuits. These systems are designed to operate at approximately 20 suns. This is also a technically proven approach but this approach also suffers from the investment problem. Here, investment is again required for special lenses, trackers, and thermal management systems. Here, the plan is that the cells will be available from the cell suppliers who make planar arrays. However, this presents two problems. The first problem is that the planar cells have to be significantly modified to operate at 20 suns. The second problem is that the planar cell suppliers are not motivated to cooperate. For example, suppose that the concentrator approach proves to be cheaper and the market expands by three times. The problem for the planar cell suppliers is that their part will actually shrink by 3/20 times. Again, these systems are not cost effective unless made in large sizes and in large volumes and there are no intermediate markets other than the utility scale market.
The third approach to solar concentrator systems was initiated by the planar module manufactures. Realizing that if their one sun planar module were operated at 1.5 suns, they could produce 1.5 times more power and consequently reduce the cost of solar electricity by 1.5 times, they built a system using edge mirrors to deflect sunlight from the edge areas onto their panels. Unfortunately, this approach was technically naive. The problem encountered was that the modules then absorbed 1.5 times more energy and there was no provision to remove the additional heat. This then affected the module lifetime.
Solar concentrators require very high investments to scale up production of a new concentrator cell. The investment required for manufacturing scale-up versions of a new cell is prohibitive. Another problem that needs to be solved is the cell-interconnect problem.
There is a need for a solar concentrator module that is a retrofit for a planar module and that is easier and cheaper to make. The business infrastructure for trackers and lenses should already be in-place. The heat load should be easily manageable. Investment requirements should be manageable and it should not threaten existing cell suppliers. Cells to be used should be available with very minor changes relative to planar cells. Therefore, low cost cells should be available from today's cell suppliers. Finally, it should be usable in early existing markets in order to allow early positive cash flow.